Antenna



Oct. 25, 1955 ALLEN s. ouwam United States Patent O ANTENNA Allen S. Dunbar, Brookline, Mass. assigner, by mesne assignments, to the Uniited Slates of America as represented by the Secrelary ol W a1 Applicafion January 3, 1946, Serial N0. 638,837

10 Clainra (Cl. 25fi33.63)

This invention relates to antennas and more partieularly to an antenna adapted t produee a predeterrnined radiation pattern.

It is freqnently desirable to cause the radiation ernannting frorn an antenna to illuminate a portion of space With a predetermined radiation pattern. t is particularly desirable in certain instances, for exarnple in radie objeet locating systems in whieh a Single antenna rnay serve both for transrnission cf electrornagnetic radiation and for reception of eehees, to produee a radiation pattern such that 0ajects in a given plane and having like reflectivity will produce equal echoes regardless cf the location of the objects in that plane. Such antennas are particularly useful in airborne radio echo detection apparatus when it is desired that echoes frorn ground objects of like reflectivity shall have the same intensity regardless of the locaticns the ebjects. lt may readily be proved that the radiation intensity frorn such an antenna should be proportional to the cso A where angle A indicates the angle of radiation as measured frorn a horizontal plane through the antenna.

Therefore, among the objects of this invention are: to provide an antenna Which will produce a cse radiation pattern; t0 provide an antenna which Will produce a desirecl predetermined directional radiation pattern; and to provide such an antenna adapted for utilization with a line source of radiation.

Further objects, advantages, and nevel features of the invention Will become apparent from the descriptien con tained herein Wherein reference is made to the accompanying drawing in which:

Fig. 1 is a perspective view of a preferred embodiment of the invention, and

Fig. 2 represents a side view cf one of the wave guide plates of the antenna structure.

It is conternplated in the invention to feed a parallel plate wave guicle assembly with electromagnetic energy having polarization parallel t0 the plane of ll6 wave guicle plates. The wave guide assembly alters the phase velocity of energy traveling therethrough, and suitable shaping of the guide surfaees produces a desired radiation pattern.

Referring now to Fig. 1, a hollow pipe wave guide 5 introduces electrornagnetic energy frorn source (not shown) to a parabolie pillbox e. Pillbox 6 is eenstructed of parallel wave guide plates 8 and a parabolic cylindrieal reflecting surface *i substantially normal to the plates. Energy from wave guide 5 is introduced near the focus of-the inner parabolic surface cf reflector 7 and radiation having a substantially straight line phase froni is seeured along pillhox aperture S. Aperture 9 may be flared, if desired, fer i1npedance matehing and energy direeting purposes. Et Will be elear to those skilled in the art that aperture 9 may be shaped so that energy emanating therefrorn prevides substantially a line saure-e 0f radiation Which is normal to the axial plane of the parabolic eylindrical refleeting surface 7.

'For convenience in description, line lilalong aperture 9 may be assi1rned as the line source 0f radiation. It will 2,721,940 Patented Oct. 25, 1955 2 also be assumed that it is desired to illuminate a ground plane with a csc radiation pattern. The antenna stracture shown in Fig. 1 and the corresponding end view cf Fig. 2, in which line source 10 is oriented parallel to the ground plane, indicate the correct orientation ef the antenna to accomplish this result. The energy ernanating from source 10 is polarized in a particular plane 01 along particular lines, which, in this instance, are perpenclicular to the pillbox plates 3 and likewise to line ll. A plurality of parallel plate wave guides 11 are formed oy an assembly 12 of conduetively surfaced plates 13. Plates 13 may be secured to end members 14 and 15 attached to a supporting structure (not shown) Which also supports pillbox 6 and wave guide 5. Bracing menibers nray be provicled for pillbox 6 on its upper plate 8 as shown. The conduetive surfaces of the plurality of parallel plate wave guides 11 thus forrned are oriented parallel to the plane of polarization of the radiant energy, that is, perpendicular to line source 10.

Referring now to Fig. 2, the leading or near edges 16 of these conductive surfaces, that is, the edges nearest line source 16, are circular in shape so that each edge lies on a circular cylindrical surface having line 16 as its axis. The far edges 17 of these concluctive surfaces, that is, the eclges farthest from line source l, are shaped to produce the desired radiation pattern effect, as will appear more fully hereinafter. Edges 17 lie 011 a cylindrieal surface, not necessarily circular, having line elements parallel to line 10.

An energy phase front departing frorn line source 10 is circularly cylindrieal in configuration, and therefore energy reaehes edges 16 of parallel plate guides 11 in phase.

The arrowed lines in Fig. 2 display directions of travel cf the energy. As is well known, the spacing between plates 13 will determine the phase veloeity of the electromagnetic energy passing therebetween. Because the energy leaving source 10 reaches the leading edges 16 of the wave guides along a phase front, the phase freut will undergo no alteration and the energy will continue to travel along straight lines as illustrated by arrowed lines 18 and 19. However, upon passing from wave guides 11 into the atmosphere beyond edges 17 at which the phase velocity again changes, the phase front will nndergo an alteration due to the varying path lengths within wave guides 11. Since phase velocity in the parallel plate wave guides 11 is greater than the veloeity of eleetrornagnetie energy in air, thephase freut emanating from any portion of the wave guide structure 12 along the far edges 17 will undergo a change in direction towarcl the normal of the cylindrical surface 011 which eclges 17 lie. The shape of edges 17 may be eornputed by direct mathematical or graphical methods. For example, a radiation pattern of the csc type may oe aehieved by computing the shape of edges 17 utilizing analogous optical methods. Sinee the ratio ef the velccity of radiation in the guides to the velecity 0f radiation in air may be determined frorn the spacing between the plates, a eorresponding coefileient of relractlon er delectric constant is readily obtained. An equation for the design of the outer edges 17 is:

for producing the desire-zl csc pattern. The upper per tions 0f edges 17 are then nearly hyperbolic, the feeus of the hyperbola being at line ll. In the equation as indicated for a chosen point 21, r is the radial distance from line 10 to outer edge 17; ro is a constant;.a is the angle that (anergy incident on the Eintenna lei1s 'maks with the horizontal; is the angle between the direction of travel of energy emerging from the lens and the horizontal, in other words the direction of the emerging beam; and u is the equivalent dielectric constant cf the antenna lens system.

An advantage of the described embodiment is its production of a csc patern of radiation over large angles of elevation, heretofore not readily attainable.

Although the description herein has been With reference to the transmission of electrornagnetic energy, it will be understood by those skilled in the art that the antenna may equally well be used for purposes of reception With like directive characteristics.

Furthermore, it will be apparent to those skilled in the art that there are many variations of the invention. Therefore, it is not desired to restrict the scope of the invention to the precise embodirnent herein described laut to include all modifications or equivalents which conforrn to its spirit.

What is claimed is:

l. An antenna for the transfer of electromagnetic energy, including a plurality of substantially planar and parallel conductive plates separated substantially equal distances to form wave guides, each said plate having a first curved edge and a second curved edge, said first curved edges lying 011 a first cylindrical surface, the axis of said first cylindrical surface being perpendicular to the planes of said plates, said second curved edges lying on a second cylindrical surface, the axis of said second cylindrical surface also being perpendicular to the planes of said plates, the width of said plate, between said curved edges, varying from point to point along the length of said plate, whereby energy having a given field pattern polarized in the plane of said conductive plates and incident 011 said first cylindrical surface is refracted in passing through said wave guides to forrn a desired field pattern upon emerging frorn said second cylindrical surface.

2. The antenna of claim 1 wherein one of said cylindrical surfaces is circularly cylindrical.

3. An antenna as defined in claim l, Wherein the first cylindrical surface is circularly cylindrical, and further including a source of electromagnetic waves and means for causing said waves to form a cylindrical wavefront about the axis of the first circularly cylindrical surface with the said waves polarized parallel to the said conductive plates.

4. An antenna as claimed in claim 3, wherein the second said cylindrical surface corresponds to the equation:

T log.

wherein r is the radial distance from the axis of said circularly cylindrical surface to a point on said second cylindrical surface, ro is a constant, o: is the angle that a ray of said electromagnetic energy incident on said circularly cylindrical surface makes with a line bisecting said circularly cylindrical surface, said line being perpendicular to the axis of said circularly cylindrical surface, 0 is the angle that a ray emerging frorn said second cylindrical surface makes with said bisecting line, and u is the equivlent dielectric constant of said wave guides, whereby an approximately csc field pattern of radiation over a large range of angles in the planes of said plates is derived from the electromagnetic energy having a cylindrical Wavefront about the axis of said first circularly cylindrical surface.

5. A plurality of plate elements having conductive surfaces symmetrically placed and substantially equally spaced to form parallel plate wave guides, each plate having a first curved edge and a second curved edge, said curved edges being opposed to each other, the width of said plate, between said curved edges, varying from point to point along the length of said plate, the corresponding curved edges of each consecutive pair of said plates defining opposed curved orifices of the wave guide formed between said plates, said wave guide including said orifices being substantially free from conductive material, whereby electromagnetic energy, having a given field pattern and polarized parallel to said plate elements incident on said first curved edges, is refracted in passing through said wave guides to forrn a desired field pattern upon emerging from said second edges.

6. A metallie lens systexn for altering the field pattern of eleetromagnetic euergy, including a plurality of parallel plates forming wave guides, each plate having a first curved edge and a second curved edge, said curved edges being opposed to each other, the Width of said plate, between said curved edges, varying from point to point along the length of said plate, whereby electromagnetic energy polarized parallel to said plates and incident on said first curved edges is refracted in passing through said wave guides 7. A lens comprising a pair of spaced parallel flat conductive members having a set of corresponding circular longitudinal edges and a set of corresponding hyperbolic longitudinal edges, said circular edges being parallel and said hyperbolic edges being parallel.

8. A lens comprising two spaced parallel flat conductive members, at least one of said members having two oppositely-disposed longitudinal edges, the curvature of one of said edges being circular, the curvature of the other of said edges being hyperbolic, the other of said members being of at least equal dimensions and area as said one of said members whereby the space included between said two members will be of uniform thickness determined by the spacing between said parallel members and will have two oppositely-disposed longitudinal contours having curvatures determined by the said oppositely-disposed longitudinal edges of said one member.

9. An antenna for the transfer of electrornagnetic energy including a plurality of substantially planar and parallel conductive plates separated substantially equal distances to form wave guides, each said plate having two oppositely-disposed longitudinal edges, at least one of said edges having a curvature concave throughout a major portion of its length and convex throughout the remainder cf its length near one end of said plate, the corresponding longitudinal edges of all said plates being substantially parallel, the set of curved longitudinal edges of said plates lying on a cylindrical surface the longitudinal axis of said cylindrical surface being perpendicular to the planes of said plates, the other set of longitudinal edges of said plates lying on a smooth surface the longitudinal axis of said smooth surface also being perpendicular to the planes of said plates, the width of each of said plates between said oppositelydisposed longitudinal edges varying from point to point along the length of said plate, whereby energy having a given field pattern, polarized in the plane of said conductive plates and incident on one of said surfaces is refracted in passing through said wave guides to form an approximately cosecant squared pattern of radiation over a large range of angles in the planes of said plates.

10. A radio wave refractor for linearly polarized radio waves, comprising a first conductive flat plate, a first edge of said plate having a circularly concave curvature and a second edge of said plate, oppositely-disposed to said first edge, having a hyperbolically concave curvature, the area of said first plate being at least coextensive with the area between said first and said second edges and straight lines joining corresponding ends of said edges, a second conductive flat plate disposed in a plane parallel to that of said first plate, the lengths cf said circular and hyperbolic edges of said first plate both being large with respect to said separation between said plates, said second plate being at least coextensive with the normal projection of said first plate on the plane in which said second plate is disposed, said plates defining betweeu them a wave guide having a first circularly curved concave orifice and a second oppositely-disposed orifice which is hyperbolically curved and concave, whereby linearly polarized radio waves having a polarization parallel to the planes of said plates, and a particular shape of wavefront, when incident 011 one of said orifices and directed generally toward the other cf said orifices, Will be refracted in passing through said wave guide to form a desired field pattern upon issuing from the other of said orifices.

References Cited in the file of this patent UNITED STATES PATENTS Southworth Aug. 6, 1946 Feldman Dec. 3, 1946 Barrow Feb. 18, 1947 Hansell Iuly 8, 1947 Iams Inne 8, 1948 

